Diagnostics and therapy of vestibular schwannomas – an interdisciplinary challenge

Vestibular schwannomas (VS) expand slowly in the internal auditory canal, in the cerebellopontine angle, inside the cochlear and the labyrinth. Larger tumors can displace and compress the brainstem. With an annual incidence of 1:100,000 vestibular schwannoma represent 6–7% of all intracranial tumors. In the cerebellopontine angle they are by far the most neoplasm with 90% of all lesions located in this region. Magnetic resonance imaging (MRI), audiometry, and vestibular diagnostics are the mainstays of the clinical workup for patients harboring tumors. The first part of this paper delivers an overview of tumor stages, the most common grading scales for facial nerve function and hearing as well as a short introduction to the examination of vestibular function. Upholding or improving quality of life is the central concern in counseling and treating a patient with vestibular schwannoma. Preservation of neuronal function is essential and the management options – watchful waiting, microsurgery and stereotactic radiation – should be custom-tailored to the individual situation of the patient. Continuing interdisciplinary exchange is important to monitor treatment quality and to improve treatment results. Recently, several articles and reviews have been published on the topic of vestibular schwannoma. On the occasion of the 88th annual meeting of the German Society of Oto-Rhino-Laryngology, Head and Neck surgery a special volume of the journal “HNO” will be printed. Hence this presentation has been designed to deviate from the traditional standard which commonly consists of a pure literature review. The current paper was conceptually woven around a series of interdisciplinary cases that outline examples for every stage of the disease that show characteristic results for management options to date. Systematic clinical decision pathways have been deduced from our experience and from results reported in the literature. These pathways are graphically outlined after the case presentations. Important criteria for decision making are size and growth rate of the tumor, hearing of the patient and the probability of total tumor resection with preservation of hearing and facial nerve function, age and comorbidity of the patient, best possible control of vertigo and tinnitus and last but not least the patient’s preference and choice. In addition to this, the experience and the results of a given center with each treatment modality will figure in the decision making process. We will discuss findings that are reported in the literature regarding facial nerve function, hearing, vertigo, tinnitus, and headache and reflect on recent studies on their influence on the patient’s quality of life. Vertigo plays an essential role in this framework since it is an independent predictor of quality of life and a patient’s dependence on social welfare. Pathognomonic bilateral vestibular schwannomas that occur in patients suffering from neurofibromatosis typ-2 (NF2) differ from spontaneous unilateral tumors in their biologic behavior. Treatment of neurofibromatosis type-2 patients requires a multidisciplinary team, especially because of the multitude of separate intracranial and spinal lesions. Off-label chemotherapy with Bevacizumab can stabilize tumor size of vestibular schwannomas and even improve hearing over longer periods of time. Hearing rehabilitation in NF2 patients can be achieved with cochlear and auditory brainstem implants.

published on the topic of vestibular schwannoma. On the occasion of the 88 th annual meeting of the German Society of Oto-Rhino-Laryngology, Head and Neck surgery a special volume of the journal "HNO" will be printed. Hence this presentation has been designed to deviate from the traditional standard which commonly consists of a pure literature review. The current paper was conceptually woven around a series of interdisciplinary cases that outline examples for every stage of the disease that show characteristic results for management options to date. Systematic clinical decision pathways have been deduced from our experience and from results reported in the literature. These pathways are graphically outlined after the case presentations. Important criteria for decision making are size and growth rate of the tumor, hearing of the patient and the probability of total tumor resection with preservation of hearing and facial nerve function, age and comorbidity of the patient, best possible control of vertigo and tinnitus and last but not least the patient's preference and choice. In addition to this, the experience and the results of a given center with each treatment modality will figure in the decision making process. We will discuss findings that are reported in the literature regarding facial nerve function, hearing, vertigo, tinnitus, and headache and reflect on recent studies on their influence on the patient's quality of life. Vertigo plays an essential role in this framework since it is an independent predictor of quality of life and a patient's dependence on social welfare. Pathognomonic bilateral vestibular schwannomas that occur in patients suffering from neurofibromatosis typ-2 (NF2) differ from spontaneous unilateral tumors in their biologic behavior. Treatment of neurofibromatosis type-2 patients requires a multidisciplinary team, especially because of the multitude of separate intracranial and spinal lesions. Off-label chemotherapy with Bevacizumab can stabilize tumor size of vestibular schwannomas and even improve hearing over longer periods

Introduction
Vestibular schwannomas are benign tumors growing typically in the internal auditory meatus and in the cerebellopontine angle. Still the term of acoustic neuroma is used, which is strictly speaking not correct, but has been coined wrongly in medical language. Today, this type of neuroectodermal tumor is called vestibular schwannoma because it develops from the Schwann cells of the vestibular root of the vestibulocochlear nerve [1], [2]. It is a slowly growing tumor and displaces other structures. In cases of bilateral occurrence, it is always defined as neurofibromatosis type 2 (NF-2) [3], [4], [5], [6]. These tumors have to be differentiated from vestibular schwannomas with regard to their biological and clinical characteristics. They show a highly variable growth behavior and are associated with other tumors, among others with gliomas and meningiomas [1], [7], [8]. Vestibular schwannomas represent about 6-7% of all intracranial tumors, however, with 90% they are the most frequent lesion appearing in the cerebellopontine angle [9]. The annual incidence amounts to 1:100,000. The tumor may appear generally in every age of life, but the main manifestation is between the 3 rd and 5 th decade [10]. Regarding the gender distribution, contradictory data are found in the literature. Brown et al. mention a majority of female patients and assume a hormonal process for the development of vestibular schwannomas [11]. Other authors do not find differences regarding the gender distribution [12], [13], [14]. In the focus of counseling and treatment of patients suffering from vestibular schwannomas is the permanent maintenance or improvement of the quality of life. Hereby, multiple factors play a crucial role, e.g. from organ-related symptoms such as hearing loss, functional disorder of the facial nerve, vertigo, vestibular disorders, tinnitus, via the fear of a growing tumor that had remained in situ or residual findings during decades of follow-up controls up to social factors such as invalidity as well as social isolation. In principle, depending on the size, there is no imperative need to treat an asymptomatic, non-growing vestibular schwannoma. In contrast, for example the removal of a small tumor from the cerebellopontine angle is an excellent chance to preserve the hearing ability of an affected patient and thus his quality of life. The patient's decision to undergo treatment or not depends on various factors and may be completely different for the same tumor entity and the same symptoms, even if the medical counselor transmits always the same information during the conversations. In the following, the diagnosis and classification of the disease will be described. This article does not include methodical-technical aspects of the treatment (microsurgical techniques, approaches, intraoperative monitoring, or dose determination in radiosurgery) in order to keep the manuscript coherent and clear. In this way, there was space for a systematic series of case examples that complete already published statistics by their clarity and present current possibilities and treatment outcomes descriptively.

Imaging diagnostics
Magnetic resonance imaging (MRI) is the method of choice for detection, staging, and follow-up of vestibular schwannomas. The examination should be performed with high-field MR systems (1.5-3 Tesla field strength) with dedicated surface coils. A typical scan protocol consists of FLAIR (fluid attenuated inversion recovery), T1-weighted (T1-w) spin echo (SE) or turbo spin echo (TSE) before and after application of contrast media and thin-slice (=1 mm) T2-weighted 3D gradient echo (e.g. CISS = constructive interference in a steady state; FIESTA-C = fast imaging employing steady state; …), or 3D-TSE (e.g. SPACE = sampling perfection with application optimized contrasts using different flip angle evolution; VISTA = volume isotropic turbo spin echo acquisition; CUBE) sequences. A diffusion-weighted sequence can be performed optionally to exclude/confirm acute ischemia. Mainstay is the thin-slice T2-w 3D sequence that shows high contrast between liquor on the one hand and nerves, vessels, and bone on the other hand and thus has a cisternographic effect. The acquired images can be reformatted in arbitrary orientation because of the isotropic resolution. It is suitable for exact tumor volumetry in the follow-up as well as for preoperative assessment of the tumor in relation to the brainstem, the fundus, the vessels and nerves. Furthermore, the assessment of the inner ear is best achieved with this sequence type [15], [16], [17]. The high-resolution T1-w sequence before and after application of contrast agent facilitates the detection of very small tumors and the postoperative evaluation, especially the differentiation between scars and residual tumor tissue or recurrences. The FLAIR sequence that covers the entire neurocranium, is used as an overview sequence to exclude other pathologies. If appropriate, a T1-w sequence with contrast agent assessing the entire neurocranium can be added to detect lesions affecting the blood-brain barrier or meningiomas (e.g. in the context of NF2). In order to allow for an objectively well traceable follow-up of the tumor size, the examination protocol should be standardized and measurements should be saved in PACS.

Management of the disease
Regarding the management of the disease, numerous articles have been published, among others there is a recent review article in the German journal HNO that reflects the state-of-the-art based on the relevant international literature. Hence, we decided to focus in this article less on theory but mostly on practice and interdisciplinarity. In the past, many dogmas overshadowed the treatment of patients with vestibular schwannomas. In the times of microsurgery, for a long time the complete tumor resection was considered as most important to avoid tumor recurrences, sometimes even at the expense of functional preservation. The introduction of stereotactic irradiation and the associated possibility to achieve growth interruption of the tumor for a high percentage with at the same time a low rate of side effects, further increases the claims to microsurgical treatment. Today, the preservation of the neuronal function is most relevant. However, it must not be forgotten that this aim can often be achieved with complete tumor resection. For this reason, it is often not possible to develop ex ante the ideal treatment concept for an individual patient. Recurrences occur after surgery and also after irradiation; even bi-modal, combined treatments are not always successful. Even if a patient had a treatment outcome with a low risk of recurrences and good hearing, persisting tinnitus and vertigo might be remaining disorders that are difficult to tolerate. The management of the single patient will always require an individual concept that will have to be adjusted during the further course ( Figure 1). Figure 1: Options for the management of patients with vestibular schwannomas. Generally, for individual patients a combination of the 3 management pillars and at different times a switch from one modality to another is possible. So a primarily growing and then micro-or radiosurgically treated vestibular schwannoma may first be observed and in cases of recurrent growth, the other treatment procedure may be applied.
This complexity makes it so difficult to create standardized treatment pathways for this disease. So it seems more important to establish a continuous interdisciplinary dialogue than to establish standards. Being open for treatment concepts that go beyond the control or removal of the tumor and that are oriented at the patient's quality of life, as well as scientifically elaborating new diagnostic and therapeutic options will determine the future. This present article was conceived around a case collection, in which the reader will find examples for every stage of the disease describing the current microsurgical and radio-therapeutic options of disease management. After the case series, suggestions are found for a classification regarding a reasonable and suitable management of the disease in the sense of decision cascades and clinical treatment pathways. Furthermore, factors are discussed that significantly influence the quality of life of patients suffering from vestibular schwannomas. There will also be an overview about the management of those tumors in patients with neurofibromatosis type 2.

Tumor stages
Tumor size and expansion play a crucial role in terms of the staging. Several authors have correlated these two criteria with different surgical approaches and treatment indications and outcomes [18]. As an example, the classification of Samii is cited here that -as the one of Koos [19] -differentiates mainly 4 tumor stages, however, especially patients in stage 4 are further differentiated regarding the presence of occlusion hydrocephalus [9], [20] (Figure 2).

Classification of the hearing ability
As an example for a systematic classification of the hearing function, the guideline of the American Academy of Otolaryngology -Head and Neck Surgery (AAO-HNO) is mentioned [21]. It stages 4 "classes" of hearing ability; class A and B describe a still functional hearing that the patient may use in daily life. The classification is performed based on a pure tone audiogram, of which an The columns represent the percentage of the changes of speech discrimination, the lines represent the average level changes in the speech range of the tone audiogram. An improvement of the hearing ability is improbable; hence the results are in the inferior left quadrant (modified according to [22]).
average hearing loss is calculated over the frequencies 0.5, 1, 2, and 3 kHz (dB value in front of the decimal point) and based on a speech discrimination test indicating the percentage of words that are recognized at a volume of up to 40 dB above the hearing threshold or at maximally tolerable loudness (value behind the decimal point; normally hearing people recognize 100% of the words at 50 dB and more): • Class A (≤30 dB, ≥70%) • Class B (>30 dB ≤50dB, ≥50%) • Class C (>50 dB, ≥50%) • Class D (arbitrary, <50%) According to this classification, functional hearing is only present in the classes A and B. Regarding data collection in the speech discrimination test, standardization would be desirable, but currently it cannot be achieved. Ideally, a validated word list of at least 50 words in the patient's mother language should be used, which is offered at a standardized level of 40 dB above the hearing threshold or maximally tolerable loudness [22]. In prospective studies or single centers, such a standardization is possible, in the practice still a certain heterogeneity of the data acquisition has to be tolerated. To describe the outcome regarding the hearing ability in a trial, pre-and postinterventionally established cross tables are an option. The columns display the speech discrimination and the lines the pure tone audiometry ( Figure 3). Such cross tables allow assessing the study results relatively clearly at a glance.

Vestibular diagnostics
For the diagnosis as well as post-therapeutic follow-up of patients with vestibular schwannoma, vestibular diagnostics play a key role. In the context of pre-therapeutic examinations, the ENT-specialist is highly involved not only in the evaluation of the cochlear function and the function of the facial nerve, he is also responsible to find the exact diagnosis or the exclusion of a certain disease in cases of vertigo symptoms. Even if nearly all patients report about the main symptom of unilateral hearing loss and tinnitus, about 10-15% of the patients suffer from initially unclear vertigo without hearing loss or tinnitus so that nearly all patients seek advice -sometimes by making some detours -of an otolaryngologist. The low number of patients who initially complain about vertigo as single symptom and who are then diagnosed of vestibular schwannoma in the further course, may be explained by the slow growth of schwannomas and hereby sufficient time for central compensation. If vertigo is observed, patients often describe unsystematic uncertain gait with possible increase in the dark or drift tendency to one side; frequently, they only mention it when they are specifically asked. An exact anamnesis of possible vertigo complaints requires sufficient time and attention as every vestibular test does, i.e. also for patients with vestibular schwannoma. In particular after surgical therapy of vestibular schwannoma, patients report about acute vertigo attacks and postural instability. The intensity and severity of the postoperative vertigo is directly proportional to the preop-erative vestibular function that has to be determined before surgery by means of extensive vestibular testing. After clinical examination with Frenzel goggles, those examinations encompass also video-nystagmography at rest or after provocation by head shake, orientation and position test under video-nystagmography, caloric test, video head impulse test, examination of the vestibular evoked myogenic potentials as well as an examination in the rotating pendulum chair and an extensive functional testing, for example by means of sensory organization test. Such a complete test battery requires time and staff and a good cooperation by the patient. If those preconditions are not fulfilled or available, the video head impulse test with testing all semicircular canals together with the VEMP testing of sacculus and utriculus already provides a good and time-efficient overview of the function of the peripheral vestibular organ performed by an experienced examiner and allows possible conclusions regarding the already damaged part of the vestibular nerve. In this way, the exact condition of the actual peripheral vestibular function can be measured and a possibly existing central affection in cases of large vestibular schwannomas as well as an already existing compensation can be revealed. Thus a good estimation of the functional postural situation is obtained. Especially patients with bilateral vestibular problems can be identified who have to expect a severe and complicated postoperative course of the disease. In those cases, special preoperative information and counseling have to take place. If necessary, surgery of a vestibular schwannoma has to be postponed or it seems to be more appropriate that the patient undergoes radiotherapy. On the other hand, it is useful that patients with single-sided preoperative vertigo concerning the side of the schwannoma rather undergo surgical therapy because after transection of the vestibular nerve in the context of resection a better central compensation may probably be achieved. So extensive vestibular diagnostics also play a crucial role for making the best therapeutic decision. But also the possibility to inform patients about the expected postoperative complaints gains in importance with regard to current medico-legal aspects. In general, the vestibular rehabilitation should be introduced very early in the postoperative phase and the patients are invited to undertake as many activities as possible that occupy the vestibular system. It is recommended to provide specific exercise instructions teaching the patients how to include balance exercises as often as possible in their daily life and to perform those exercises also with closed eyes to exclude the merely visual compensation. Also professional physiotherapy and exercise instructions as well as training by means of sensory neuro-feedback methods seem to be beneficial to achieve a rapid central compensation of postoperative vertigo. In this way, the re-integration into daily life can be achieved rapidly and in general the patients are free of complaints after 6-9 months.
Beside the regular follow-up of the cochlear function, hearing rehabilitation, and imaging, also a short standardized checkup of the vestibular function should be performed in order to document a course of central compensation in the years after therapy. In cases of deterioration, possibly developing recurrence etc., vestibular diseases may be identified earlier.
In summary, preoperatively, the high value of sufficient vestibular diagnostics allows better information and counseling about different therapeutic options and expected side effects; and after therapy, the central objective to provide a quality of life as high as possibly can be achieved.

Function of the facial nerve
In the context of larger tumors, the function of the facial nerve is often impaired, which has an influence on the treatment approach. To assess the degree of neural paresis, the classification according to a proposal of William House and Derald Brackmann from 1985 could be internationally established (Table 1). Regarding further pre-and intraoperative diagnostic procedures (e.g. electrophysiological examination procedures such as acoustically evoked brainstem potentials) extensive literature on this topic has been published and will not be further discussed here.
8 Surgical approaches 8.1 Transtemporal approach (middle fossa approach) The transtemporal approach via the middle fossa is suitable for intrameatal and low-grade extrameatal tumors up to a size of 20 mm and patients with residual hearing [23]. The patient is lying in supine position, the head is slightly overstretched and turned to the contralateral side. Preauricular incision is performed starting from the level of the tragus nerve up to about 5 cm above the auricle in the temporal region. After preparation of the fascia of the temporal muscle and craniotromy, the temporal flap can be lifted and the internal auditory meatus is exposed in top view of the temporal bone and can be opened [24]. In neurosurgery, it is called the subtemporal approach because it refers to the temporal flap of the brain which should not be touched during surgery if possible.

Translabyrinthine approach
The translabyrinthine approach is suitable for patients with tumors that have already destroyed the hearing ability. Beside dissection of the internal auditory meatus, mastoidectomy as well as labyrinthectomy are performed. The advantages are the secure exposition of the facial nerve and the overview of the posterior fossa. The patient is lying in supine position and the head is turned to the contralateral side. After retroauricular, C-shaped incision and mastoidectomy exposing the sigmoid sinus, the dura of the posterior fossa as well as the facial nerve in its bony canal in the area of the second knee, and the labyrinthine bloc, first the lateral semicircular canal is drilled out, then the posterior and finally the superior semicircular canals follow. Afterwards, the vestibulum can be opened and the internal auditory meatus is exposed. The exposition and opening of the dura are performed until the intervention reaches the cerebellopontine angle [25], [26].

Retrosigmoid approach
The retrosigmoid approach is especially suitable for tumors with larger extrameatal parts. It allows a secure and wide exposition of the posterior fossa and thus tumor resection with hearing preservation [27]. The facial nerve is exposed in the internal auditory meatus and at the brainstem, its further course at the ventral tumor side is only visible in the last step of the preparation [28], [29], [30]. In cases of smaller tumors, the patient is lying in supine position, the head is turned to the contralateral side and slightly inclined to the breast. In cases of larger tumors, the surgery site often has to be continuously rinsed and the irrigation fluid and the blood have to drain off, so that the patient may be positioned in a beach chair position; however, hereby the risk of air embolism is rather high [31]. The incision describes a bow and starts above the auricle and ends behind the mastoid tip. After exposition of large emissary veins during craniotomy, the incision of the dura is performed alongside the sigmoid and transverse sinus. After opening the arachnoid mater in the area of the cerebellomedullaris cistern and draining off liquor, the cerebellopontine angle is exposed and the internal auditory meatus can be opened.

Illustrating cases
Instead of repeating findings that are published in the literature in a dry and manual-like manner, this contribution wants to convince mainly with a clear description of a case series and give ideas and hints for optimal information and treatment of affected patients. According to the title of this article, those are exclusively cases in which at least the course of the disease justified treatment. Of course, especially in the context of older patients, most centers will first observe the spontaneous course by regularly performing clinical and imaging examinations. The annual -non-volumetric -growth rates of the tumors reported under strict observation varied between 0.3 and 4.8 mm [32], [33], [34]. Interestingly, the growth rate of a tumor seems to be a more reliable predictor for threatening hearing loss than the absolute tumor size at the time of diagnosis. In a meta-analysis of 982 patients,  found out that patients with a tumor growth of less or equal 2.5 mm had a clearly higher preservation rate for their hearing ability (75% vs. 32%, p<0.0001), independent from the original size of the tumor [35]. If the indication for treatment is made in patients that were initially observed, it occurs in 75% of the cases within the first 5 years [32].
In order not to extend the volume of this article, spontaneous courses will not be included in the case series. Some spontaneous courses of the disease, however, will be described based on tumors that were treated later. Furthermore, a differentiation was made between primarily surgical and primarily radiotherapeutic cases in order to demonstrate as clearly as possible the possible effects of the treatment modalities. The examples of this case series are systematically classified according to the functional hearing abilities of the patients and previous treatment (surgery or irradiation).  • Intra-and minimally extrameatal vestibular schwannoma located near the fundus, measuring 9x5x5 mm ( Figure 5 and Figure 6) Intervention: • Transtemporal resection with monitoring of the facial nerve and intraoperative BERA on September 16, 2010 Course: • No postoperative vertigo • Facial nerve: House-Brackmann grade II; normalization within 8 weeks • Class A; unchanged compared to surgery  • No tinnitus • 5 years after surgery, no recurrences ( Figure 6) No functional hearing ability Case #3, male, age: 47 years History: • In May 2013, the patient woke up in the morning with an acute vestibulo-cochlear disorder on the right side. First, severe rotational vertigo with subjective deafness and significant tinnitus on the right side. During therapy with cortisone, the tinnitus improved and the vertigo complaints were regressive. The attempt to perform external round window covering on the right side did not lead to improvement of the deafness.
Clinical findings: • Massive cochlea-vestibular disorder with labyrinth failure and right-sided deafness. Inconspicuous status of the vestibular nerve ( Figure 7) Intervention: • Translabyrinthine resection of the vestibular schwannoma on the right side with monitoring of the facial nerve and insertion of a Contour Advanced dummy into the cochlea on January 28, 2014. Course: •   Clinical findings: • Romberg's and Unterberger tests are inconspicuous • Audiometric high frequency hearing loss in both ears in the range of 2 kHz, on the right side to -60 dB, on the left side to -35 dB • Speech discrimination of 70% on the right side at 60 dB MRI: • Inhomogeneous, intra-/extrameatal tumor on the right side that has not yet reached the fundus (stage T2). CISS images clearly demonstrate a thin layer of CSF between the tumor and the brainstem ( Figure 8) Intervention: • Functional hearing preservation with complete microsurgical resection via a retrosigmoid (lateral-suboccipital) access. Functional preservation of the facial nerve (House-Brackmann grade 1) Course: • Increased vertigo for 3 weeks after surgery, especially in the context of lateral eye movements • Slightly regressive tinnitus, in particular no impairment at night • As preoperatively, the facial nerve is inconspicuous • Class A (according to AAO-HNO) • 3 years after surgery, no recurrence No functional hearing ability Case #5, female, age: 55 years History: • First presentation with known functional deafness and recurrent rotational vertigo since several months.

Stage 3
Functional hearing ability Case #6, female, age: 35 years History: • Lumbar puncture in the context of neuro-borreliosis diagnostics. • Afterwards vertigo was observed, 2 days later sudden hearing loss and tinnitus that persisted longer so that MRI of the skull was performed. • In the further course, numbness of the left side of the face was described, mainly in the innervation area of the N. V/2-3 Clinical findings: • Whispering was well heard in the left ear.
• Audiometry revealed class A hearing ability.
• Tendency to turn to the left in the Unterberger test.
• Stable Romberg's test.  Intervention: • The patient did not wish observational strategy but primary surgery. • Complete microsurgical tumor resection with preservation of the facial nerve and the cochlear nerve via a retrosigmoid (lateral-suboccipital) access. Course: • Initially, balance problems when walking fast or in the dark. • Course of a primary intra-/extracanalicular vestibular schwannoma under observation until stage T3 was reached ( Figure 12). Intervention: • Lateral-suboccipital craniotomy on the left and microsurgically complete tumor resection with preservation of the BAEP and the facial nerve. Course: • Directly after surgery, slight postural instability with undirected tendency to fall when walking faster. • Complete regression after 6 months. • Romberg's test was stable, Unterberger test without tendency to rotate. • Audiometry: after one year, increased hypoacusis over all frequencies around 10-20 dB. • In the speech field, hearing loss around 40 dB on the left. • Inconspicuous paresis of the facial nerve. • The tinnitus had first disappeared, later it re-appeared, but more rarely. • Pressure sensation and numbness in the area of the left ear.
No functional hearing ability Case #8, female, age: 54 years History: • 15 months before first presentation, tinnitus occurred as right-sided noise, 3 months later, also hearing impairment was noticed on the right side. • Infusion therapy did not improve the complaints. • MRI demonstrates a stage T3 lesion. • Vertigo with retropulsion 6 months before first presentation, later slightly improved.
Clinical findings: • Functional deafness in the right ear.
• No paresis of the facial nerve ( Figure 13). Intervention: • Lateral-suboccipital craniectomy of the right side and complete tumor resection by microsurgery with preservation of the facial nerve. Course: • Directly after surgery, sudden hearing loss of the contralateral side (left) with only slow recovery due to infusions and dexamethasone. • Persisting vertigo and tinnitus. • Romberg's test with instability and tendency to fall until 12 months after surgery, then improvement was observed. • The patient was more impaired by the right-sided hearing loss, especially in noisy environment. • Apart from that, she felt well, no paresis of the facial nerve. • 6 months after surgery, BiCROS device was applied, of which the patient was not satisfied. • Because of unclear electrophysiological findings and negative promontory test, she decided against cochlear implantation. • Finally, she was relevantly more satisfied after implantation of a bone anchored hearing prosthesis (BAHA).

Stage 4a
Functional hearing ability Case #9, female, age: 41 years History: • 10 years prior to first presentation, already sudden hearing loss on the right with complete recovery due to infusion therapy. • Because of new right-sided sudden hearing loss and whistling tinnitus, MRI diagnostics and identification of a vestibular schwannoma on the right side. • Nearly no vertigo (dance teacher!) Clinical findings: • Nystagmus to the right when looking to the left. • Instability in standing and walking tests. • In the Unterberg test, tendency to rotate to the right. • Subjectively low-grade hypoacusis on the right. • Vestibular test: caloric hypoexcitability on the right side. MRI: • Vestibular schwannoma on the right with brainstem compression without hydrocephalus ( Figure 14). Intervention: • Complete tumor resection by microsurgery with preservation of the BAEP and the facial nerve via a retrosigmoid (lateral-suboccipital) access. • Intraoperative improvement of the acoustically evoked brainstem potentials. Course: • Postoperatively, first only vertigo was observed. • 8 days after surgery, rhinoliquorrhea was found, persisting after removal of a lumbar drainage. • 14 days postoperatively: suboccipital re-craniotomy and sealing of a fistula at the right-sided internal auditory meatus. • Then still headache and facial pain for 2 days, especially around the right eye, then rapid improvement. • Immediately after surgery, House-Brackmann grade II of the facial nerve, after 3 months grade I. • Vertigo had completely disappeared after 1 year.
• Hearing ability class A as preoperatively.
• No tumor recurrence 8 years after surgery.
Functional hearing ability Case #10, male, age: 49 years History: • Increasing hearing loss for 6-7 years on the left side, in the course also pressure sensation in the ear and tinnitus (whistling sound).  MRI: • Large vestibular schwannoma with growth into the fundus of the internal auditory meatus and significant brainstem compression ( Figure 15). Intervention: • Lateral suboccipital craniotomy and subtotal tumor resection by microsurgery with leaving a narrow tumor edge at the internal auditory meatus. • Functional preservation of the facial nerve. Course: • CCT after surgery demonstrates small parenchymal bleeding in the left cerebellar hemisphere (AICA supply area) as well as blood deposits at the tentorium and the falx. • Clinically, no cerebellar symptoms.     • Ear noise on the left 1 year before first presentation, improved with pharmacotherapy, then again increasing. • Lateral suboccipital craniotomy and partial microsurgical resection of a highly vascularized tumor with preservation of the facial nerve and the cochlear nerve. Course: • Postoperatively, relevant headache symptoms, computed tomography did not reveal hydrocephalus. • Significant improvement with symptomatic therapy. • Facial nerve: House-Brackmann grade I. • Tinnitus and hearing like before surgery. • Stable gait. • 1.5 years after surgery, persisting headaches and posttherapeutic facial pain. Improvement with application of carbamazepine and gabapentin.
• MRI of the skull revealed a minimal growth of the residual tumor over 6 months.
• First MRI follow-up revealed a stable situation. 2 years later, increasing memory disorders with massive gait instability and persisting headaches. Detection of hydrocephalus and implantation of a ventriculo-peritoneal shunt system at an opening pressure of 21 cm water column.

Intervention:
• Lateral suboccipital re-craniectomy on the left side and subtotal microsurgical tumor resection with preservation of the affected facial, glossopharyngeal, abducens, and trigeminal nerves. • Between the meatus and nearly in the center of the cerebellopontine cistern, a very thin tumor layer has to remain on the facial nerve because further resection would not have allowed functional preservation of the nerve. Histology: • Schwannomas with significant regressive changes, bleedings of different times as well as slight overexpression of p53 and p21. • No anaplasia, no malignancy.  • MRI performed 6 months after surgery, did not reveal tumor recurrence.

Cystic vestibular schwannoma, stage 4a
Functional hearing loss Case #13, male, age: 43 years History: • Tinnitus rapidly progressing over 3 months and increasing hearing loss in the right ear so that finally the right ear could no longer be used for phone calls. • In addition, progressive gait instability.
Clinical findings: • Romberg's test was insecure with tendency to fall.
Unterberg test could not be performed because of tendency to fall. • High-grade hearing loss on the right. • Audiometric inner ear hearing loss, on average >-60 dB in the speech field, right-sided. MRI: • Large cystic tumor filling the cerebellopontine angle with brainstem compression and advancing into the right internal auditory meatus ( Figure 18 and Figure 19). Intervention: • Lateral suboccipital craniotomy and microsurgical partial resection of a highly vascularized tumor that relevantly split up the facial nerve. Course: • Immediately after surgery, right-sided paresis of the facial nerve (House-Brackmann grade II). • Massively increasing vertigo and in particular image fusion disorder due to gaze-evoked nystagmus to the left. It was caused by a circulatory disorder in the area of the inferior cerebellar peduncle and the cerebellar hemisphere. • Additional complication because of gout attack in the right ankle. • 6 months after surgery only slight tinnitus perceived as weak noise. • Improvement of the gait instability and still disturbed image fusion when looking straight forward as well as diplopia and blurred vision when looking to the right without visible weakness of the abducens nerve. • Rotatory nystagmus when looking to the right. Slightly delayed diadochokinesia on the right side.   9.2 Radiosurgery (RS) and stereotactic radiotherapy (SRT)

Typical courses after RS/SRT
The term of "radiosurgery" was used by the Swedish neurosurgeon Leksell for a method developed by him in the 1950ies. It was a method of high-precision conver-gence irradiation with a high dose, that is applied once. The patient's head first had to be fixed in a stereotaxy frame (about 0.3 mm precision) similar to stereotactic surgeries. Since the 1980ies, the stereotactic positioning of the patient is applied with a special, less precise mask fixation (±1-2 mm precision) than SRT for the fractioning that is used in radiotherapy. ator Novalis (BrainLAB) -because of the longer follow-ups, the case examples were mostly recruited from the population treated with the Novalis. Since October 2012, we work with the robot-assisted radiosurgery system CyberKnife (Accuray) that allows the radiosurgical precision of about 0.3 mm due to permanent image control even without frame with mask positioning. Instead of SRT, the treatment of larger tumors can be limited to 3 single irradiations, the so-called multisession radiosurgery (msRS).
First some examples of mainly typical courses will be presented (cases 1-8), then particular, atypical courses will be described that also include severe single cases (cases 9-14). MRI: • Figure 20. Intervention: • Radiosurgery (CyberKnife, margin dose of 12 Gy at 69% isodose). Course: • 6 months after the intervention, the hearing ability was unchanged. • MRI revealed the typical reaction with central contrast agent reduction and relevant contrast enhancement in the edges showing a transiently rather small tumor.
In the further course until 12/2015, regression of the reactive changes and regredient tumor size with still well-being and good hearing ability over meanwhile 2.5 years (Figure 21).
In the following case examples, the sides in the MRI series are mirrored because of the applied stereotactic planning software. Since the assessment of the course is most relevant and no information gets lost due to this exchange of the sides, the images are not displayed in a mirrored way.

Stage 2
Functional hearing loss Case #2, male, age: 68 years History: • 4 years before first presentation, surgery of a rightsided vestibular schwannoma (retrosigmoid access). • Tinnitus and occasional vertigo. • Alternating hypo-and dysesthesia of the right side of the face.
Clinical findings: • Anacusis in the right ear.
• Labyrinth failure on the right.
• Hypo-and dysesthesia in the supply area of the 2 nd trigeminal ramus (right-sided). • Paresis of the facial nerve (House-Brackmann grade III (right side). MRI: • Intra-/extrameatal tumor recurrence (16x9 mm), progressing compared to the previous examination one year before. Intervention: • Radiosurgery (linear accelerator Novalis, Brainlab, margin dose of 12 Gy at 80% isodose). Course: • 7 months after intervention, the patient reported about an improvement of the hypo-and dysesthesia of the right side of the face, the other symptoms were unchanged. • In the further course, gradual improvement of the paresis of the facial nerve and significant tumor regression confirmed by MRI ( Figure 22).

Functional hearing loss
Case #3, female, age: 64 years History: • Right-sided tinnitus for 3 years and balance disorders that have increased gradually. • Hearing loss in the right ear was first audiometrically stable with high frequency loss on the right, now increasing up to 50 dB.
• Unterberger test with severe, undirected tendency to fall, dysdiadochokinesis on the left. • Hypoacusis on the left side.
• Course: • 6 months after intervention slightly increasing hearing loss in the right ear. • Disturbed balance did not increase.   Clinical findings: • Audiometry revealed left-sided sensory hearing loss up to 80 dB in the high frequencies. MRI: • Vestibular schwannoma on the left side, in the longitudinal axis 15 mm intra-and extrameatal nearly reaching the brainstem. • Progressive growth in the further course. Intervention: • Radiosurgery (linear accelerator Novalis, Brainlab, margin dose of 12 Gy at 80% isodose). Course: • 4 months after intervention, clinically and ENT-specifically no deterioration. • In the MRI, typical central reduction of contrast enhancement. • In the further course, regression of the reactive changes and regressive tumor size in the MRI followup until 3 years after radiosurgery, then stable condition. • Slightly progressive hearing loss in the deep and middle frequencies of 50-90 dB, constant over >8 years ( Figure 24).
• Hearing ability after >7 years on the left side with pancochlear inner ear hearing loss to 85 dB at 6 kHz, in the speech field about 20 dB poorer than initial audiometry. • Clinically, further dysesthesia in the area of the left corner of the mouth and the tongue ( Figure 25).
Functional hearing ability Case #6, female, age: 24 years History: • After right-sided sudden hearing loss, MRI confirmed vestibular schwannoma on the right side.
• Then wait-and-see strategy due to complaint-free clinical findings and bilaterally good hearing ability. • The MRI follow-up showed clear tumor progression of the tumor volume from 0.86 cm³ to 1.45 cm³ ( Figure 26 ).
• Unterberger test with mild insecurity. Intervention: • The patient refused the surgery recommended by the interdisciplinary team. • Radiosurgery (linear accelerator Novalis, Brainlab). Course: • Due to vertigo and painful dysesthesia on the right side of the face, already 3 months after intervention the first control MRI was performed. It revealed an extraordinarily severe reaction with central reduction of contrast agent and increased volume. • In the further course, nearly complete regression of the complaints. • 9 years after the intervention, still good hearing ability in both ears ( Figure 27).

Stage 4a
Functional hearing loss Case #7, female, age: 67 years History: • For many years, right-sided hearing loss, finally no useable hearing ability on the right side. Intervention: • The patient refused the surgery recommended by the interdisciplinary team. • Fractionated stereotactic radiotherapy (SRT) with 27x2 Gy (Novalis, Brainlab) at a tumor volume of 6.5 cm³. Course: • 6 months after irradiation, the patient reported about unchanged compensated gait insecurity and occasional dysesthesia on the right side of the face that disappeared in the further course.        Clinical findings: • Anacusis and facial hypoesthesia of the right side.
• No paresis of the facial nerve. MRI: • Tumor recurrence on the right side, stage 4a.
• Tumor volume of 9.6 cm³. Intervention: • Fractionated stereotactic radiotherapy (SRT) with 27x2 Gy (Novalis, Brainlab). Course: • 7 months after irradiation, the patient reported about an increased hypoesthesia on the right side of the face. Labyrinth failure and anacusis on the right side were unchanged.  MRI: • The MRI showed a progressive vestibular schwannoma on the left side of stage 3, mainly extrameatal location. Intervention: The patient refused the recommended surgery • Fractionated stereotactic radiotherapy (SRT) with 27x2 Gy (Novalis, Brainlab). Intervention: • The patient refused the recommended surgery • Radiosurgery (linear accelerator, Novalis, Brainlab; margin dose of 12 Gy at 80% isodose). Course: • In the course, first increasing tumor volume from 0.6 cm³ to 1.5 cm³ after nearly 4 years; the recommended surgery was refused. Stable clinical findings and constant hearing loss. • In the further course, tumor regression with unchanged clinical findings. • The patient is fully able to work ( Figure 31).

Stage 2
Functional hearing loss Case #11, female, age: 75 years History: • The left ear was functionally deaf.

MRI:
• Progressive vestibular schwannoma on the right side, stage 2. Intervention: • Radiosurgery (linear accelerator Novalis, Brainlab, margin dose of 12 Gy at 80% isodose). Course: • First typical course with central hypointensity of the contrast agent after 6 months and then marginal regression until 3 years after intervention. • 1.5 years later, only an intrameatal residual tumor was found with unchanged clinical findings ( Figure 32). Intervention:
• Course: • After 5 months, the tumor volume appears larger with focal spots of absent contrast enhancement. In the next follow-up examination cystic involutions becomes evident, but the tumor size remains constant. • Clinically stable findings.
• One year later, significant regression to a volume of 0.5 cm³. • Subjectively neither vertigo nor balance disorders. • Less important tinnitus ( Figure 33). Intervention:

Functional hearing loss
• Radiosurgery (linear accelerator Novalis, Brainlab, margin dose of 12 Gy at 80% isodose).  Course: • Stable clinical findings with hearing aids on the left side. • After 3.5 years, recurrent tumor growth, clinically associated with functional hearing loss and increasing balance disorders. • The suggested surgery was refused, the second irradiation was performed with a margin dose of 12 Gy (80%). • The clinically painful dysesthesia occurred and convulsions on the left side of the face required pharmacotherapy and local botox injections ( Figure 34).

Stage 4
Functional hearing loss Case #14, female, age: 63 years History: • 3.5 years after resection, progressive residual tumor on the right side. • Condition after tarsorrhaphy and neuromuscular anastomosis on the right side. • Additional findings: diabetes mellitus and chronic renal insufficiency.
Clinical findings: Anacusis and complete paresis of the facial nerve on the right side.
• Significant vestibular gait disorder and hypoesthesia of the right side of the face.
• MRI: • Progressive vestibular schwannoma on the right side, stage 4, with a volume of 5.5 cm³. Intervention: • Revision surgery was refused.
• Fractionated stereotactic radiotherapy (SRT) with 30x1.8=54 Gy (Novalis, Brainlab). Course: • After 7 months, frequent pain attacks of the right trigeminal nerve, other neurological findings were unchanged. • MRI showed a severe reaction on SRT with increasing growth and surrounding edema at that time. • In the further course, first regression of the reactive changes with clinical improvement of the balance disorders and no more pain attacks ( Figure 35, Figure 36).

Wait and scan
Functional hearing ability Case #1, male, age: 40 years History: • In the context of diagnostics for headache in 2008, MRI confirming an intrameatal acoustic neuroma of the right side of less than 3 mm. • Control MRI in February 2009 revealed a constant size of about 3x2 mm. • Subjectively no vestibular disorder with temporary right-sided tinnitus and bilateral subjectively normal hearing. • Additional findings: recurrent sinusitis, otherwise inconspicuous history.   Intervention: • Wait and scan. Course: • Annual follow-up examinations in 9-12 months interval. • MRI revealed constant tumor size of 3x2x2 mm. • Tone and speech audiometry in the normal range. • The balance tests showed no hint for peripheral-vestibular disorder. • During the regular follow-up examinations, we explained and offered all therapeutic options to the patient. Because of missing clinical complaints, the patient decided for further regular tumor observation in the sense of wait-and-scan ( Figure 37).
Functional hearing loss Case #2, male, age: 73 years History: • Progressive hearing loss on the right side for several years. • Additionally, especially in the morning, slight vertigo for some months. • Beside arterial hypertension, inconspicuous anamnesis.

Clinical findings:
Inconspicuous status of the facial nerve as well as slight vestibular disorder in the morning.
• MRI: • Intrameatal acoustic neuroma on the right side with a size of 0.7x0.3 mm. Intervention: • Wait-and-scan. Course: • Annual follow-up examinations in 9-12 months intervals. • Subjective deterioration of the right-sided hearing. • First recommendation of surgical tumor resection with explanation of alternative therapeutic options by means of radiotherapy or further observation. The patient decided for clinical and MRI controls. • One year later, again subjective deterioration of the right-sided hearing as well as slightly increased vertigo symptoms. The subjectively increased hearing loss was confirmed by tone and speech audiometry. An increase of the initial hearing loss (45%) was measured now at 65% according to Röser (1980) [36] and a reduced Freiburg speech test for polysyllables as well as for monosyllables. • In the further course, balance tests did not reveal any hint for peripheral vestibular disorders.
• Over the time of the regular controls, we offered all available therapeutic options. Because of the missing tumor growth and the moderate clinical complaints that could be compensated by hearing aids regarding the hearing ability, the patient finally decided again for regular tumor observation in the sense of wait-andscan. • Over 5 years, no significant tumor growth was observed without therapy ( Figure 38).

Stage 2
Functional hearing ability Case #3, male, age: 73 years History: • First presentation in January 2007, at that time recurrent rotational vertigo had occurred for 5 years.    10 Classification for decision-making regarding treatment and treatment pathways Up to now it was not possible to define a multicenter, multidisciplinary consensus for medical management of patients suffering from vestibular schwannomas. The decision-finding diagram is meant to be a contribution to the discussion. Similar algorithms have turned out to be a good basis for decision-making in the context of tumor board. In the decision-making process, the size of the tumor, its growth rate, the possibility or probability of complete resection with preservation of the hearing function and the function of the facial nerve, the patient's age and previous diseases, the possibly good management of factors like vertigo and tinnitus that are very important for the quality of life, and finally also the patient's opinion play a crucial role. Finally, also the experience and the outcomes of the therapy center regarding the different treatment modalities influence the decision. Before discussing the treatment modality, the expert team should clarify the question if a therapy of the tumor at the actual time is reasonable or if further observation including imaging procedures at a certain time may be the best option of the patient. Table 2 describes a possible matrix for the treatment of a patient with vestibular schwannoma. In order to base a treatment on such a matrix, unbiased consideration and sincere assessment of own treatment results are required. Here, the example of a 75-year-old patient with functional hearing is displayed who has an intra-/extrameatal tumor confirmed by MRI that reaches into th cochlear fossa. The probability that the treatment of such a patient leads to immediate or delayed morbidity, is not low. Furthermore, the growth rate of the tumor is unclear and it cannot be excluded that the vestibular schwannoma will have a constant size over several years. The tumor board would then decide in this case of first manifestation to perform MRI again after 6 months. In the context of this example, observation of the tumor is expected to achieve the best result for the patient. A patient with occlusive hydrocephalus (stage 4b according to Samii [9]) will certainly be recommended to undergo (partial) resection of the tumor, regardless the age, whereas for an old patient with communicating, non-resorptive hydrocephalus the tumor might be observed after application of a shunt system in the ventricular system. Cystic vestibular schwannomas may be one of the most demanding challenges of microsurgical tumor resection, also because the affected nerves can be highly split up and run adherently at the cell walls so that also larger vessels are difficult to be separated from tumors (see also case series [37]). The following decision-finding diagrams (Figure 40 and Figure 41) simplify enormously, but they include relevant criteria and may be helpful for decision-making. Also in this context, individual factors play a crucial role; none of the described decision-finding schemes is meant to be a dogma. It is more appropriate to consider for example the volume of a tumor as criterion instead of the largest diameter, especially in cases of irregular tumors [38]. The more complex measurement of the volume is not available in all centers so that we mention here the highest tumor diameter as criterion. Especially in neurosurgical series, mostly tumors of stage 3 and 4 are found. A primarily radiosurgical or stereotactic radiotherapy for tumors with a diameter of more than 25 mm is problematic because of the frequently occurring post-interventional swelling of the tumor and the possible development of a severe peri-lesional edema [39]. Our treatment pathways do not provide such a therapeutic option for tumors measuring more than 25 mm in diameter. If already at the time of first presentation symptoms exist that are due to brainstem compression, further observation is certainly no reasonable option ( Figure 40). Tumors with a maximal diameter of less than 25 mm may be observed to draw conclusions on their biological growth behavior ( Figure 41). This may be a prognostic factor for hearing preservation as well as for the probability of recurrence development after incomplete resection.

Quality of life and preservation of the function
The quality of life of patients with vestibular schwannomas depends on a multitude of different factors. Therapeutic interventions, in particular surgeries, are often associated with a sudden break regarding the quality of life that disappears usually in the further course. Thus it is already decisive for the result of such a survey to determine the time of assessing the quality of life. The scales applied for the evaluation of the quality of life are not homogeneous and partly not even specific for this disease. Meanwhile, however, validated specific questionnaires are available for the disease such as for example the Penn Acoustic Neuroma Quality of Life questionnaire (PANQOL) [40]. In a prospective study, Carlson et al. quantify the smallest VAS difference that is perceived as significant by the patient in the PANQOL for various symptoms in the following way: PANQOL overall score: 11 points; hearing: 6 points; balance: 16 points; paresis of the facial nerve: 10 points; pains: 11 points; energy: 13 points; anxiety: 11 points; general well-being: 15 points [41]. The weighting of the single factors influencing the quality of life of patients varies enormously. Vertigo plays a key role as well as an increasing hearing loss associated with social restrictions [42]. In this context it is mostly irrelevant which primary management strategy is pursued. A recent study (538 patients; 46% stereotactic irradiation, 27% surgery, 28% wait-and-scan) considered vertigo as significant symptom for the long-term quality of life [43]. Astonishingly, persisting headaches were more relevant for the patients of this study regarding the quality of life than function of the facial nerve, hearing loss, and tinnitus. 29

Preservation of the facial nerve
In a meta-analysis including more than 25,000 patients, Sughrue et al. found a reported rate of preserved facial nerves of 85% after middle fossa approach, 81% after translabyrinthine approach, and 78% after retrosigmoid approach [44]. Since the risk of damage depends on the tumor size, its configuration, and the patient's age, significant differences in the evaluated patient populations have to be taken into account. Looking at more homogeneous cross-over studies with all tumor stages, generally in more than 90% of the cases preservation of the facial nerve is anatomically and functionally possible in the context of complete tumor resection [45], [46], [47]. At this point, it is worth mentioning a retrospective article from Erlangen published in 2001. Hereby, the authors could report about surgical treatment of 735 patients with a middle fossa approach. In this group, the average rate of preservation of the facial nerve (House-Brackmann stages I and II) amounted to 92% [48]. Already in 1997, Samii et al. could anatomically preserve the facial nerve in 930 of 1,000 patients [45]. In another study with 200 patients, the same surgeon reported about a preservation rate of the facial nerve of 98.5% after 98 complete tumor resections [46]. In cases of very extended tumors with a maximum diameter of more than 4 cm, the functional preservation of the nerve (House-Brackmann grade I-II) was successful only in 75% (n=50 [47]). Persisting paresis of the facial nerve after unilateral (radiosurgery) or fractionated stereotactic irradiation are rather rare with 1-4% [49], [50], [51]. Regarding hypofractionated radiotherapy of tumors with a diameter of >3 cm, the results with persisting high-grade paresis of the facial nerve (House-Brackmann grade III and higher) of 12 and 20% despite irradiation with a median follow-up interval of 97 months can no longer be accepted [52].

Hearing preservation
Already at the time of diagnosis, many patients do no longer dispose of functional hearing on the tumor side. In a recent study with partly observed (n=148, 28%), partly microsurgically treated (n=144, 27%), or with gamma knife (n=247, 46%) treated patients with a tumor smaller than 3 cm in diameter had a functional hearing ability on the affected side in about half of the cases (n=287, 55%) [53]. Eight years after diagnosis, this rate had decreased to less than 25% of all patients (n=105, 23%). The rate of hearing preservation in this study was highest for observed patients (68%), followed by patients with stereotactic irradiation (40%), and microsurgically treated patients (14%). Especially in cases of small tumors, however, an experienced surgeon has a good chance to completely resect the tumor and at the same time to permanently preserve the hearing ability in the affected ear [46]. For tumors of stage T1, the rate of functional hearing preservationmerely estimated based on tone audiometry -amounted to 60% of all patients; for stage T2 to 72%. In cases of T3 and T4 tumors, the rate decreased to 43%. Other authors of microsurgical series report about functional hearing preservation (pure tone audiogram with an average of <50 dB, speech discrimination >50%) in 15-40% of the cases [54], [55], [56], [57]. Also a meta-analysis (1,073 patients) showed that the hearing preservation rate in cases of intracanalicular tumors (56.9%) was better than for tumors with an extrameatal diameter of 1-9 mm (45.6%) and a diameter of 10-19 mm (32.3%) [58] [58]. Regarding the volumetric determination of the tumor size, the same trend is observed with a functional hearing preservation rate of 48% for patients with a tumor volume of <2 cm³ and only 25% for patients with a tumor volume between 2 and 4 cm³ [57]. Even very large tumors (>4 cm in maximum diameter) may be operated in single cases with preservation of the hearing ability [47]. Hence, it is also reasonable in those cases to select a surgical approach that generally allows hearing preservation. An extension of the tumor into the cochlear fossa is unfavorable regarding prognostic hearing preservation. When this region in the fundus of the internal acoustic meatus was affected by the tumor, the hearing preservation rate decreased to 47% in comparison to 76% for more medially located tumors [59]. Microsurgically, there are generally 2 approaches with which hearing preservation is possible: the retrosigmoid (lateral-suboccipital) and the subtemporal approach.

Vertigo
Vertigo is a symptom that may strongly influence the patient's quality of life. Only in the last years, it has been placed into the focus of attention [60]. Actually, the characteristics of this symptom are a predictor for the ability to work, again depending on the fact if microsurgical treatment or gamma knife surgery had been performed (2013). Apart from vertigo, in the cited study no other symptom -not even paresis of the facial nerve, hearing loss, or tinnitus -correlated significantly with permanent dependence of social benefits [61]. In a prospective study with 434 cases, Andersen et al. (2015) reported that 9% of the patients with unilateral vestibular schwannomas described severe vertigo with more than 75 of 100 points on the VAS [62]. Missing caloric irritability as well as gait and posture disorders were proportional to the tumor size. In the longer time course, the symptom of vertigo often regresses, probably due to the increasingly missing afferent nerve pathways from the unilateral balance organ [42]. Independent from this fact, further tumor growth may increase tinnitus and also unsteady gait (brainstem compression, hydrocephalus). Patients whose main problem at the time of first diagnosis was already most severe vertigo, reported about clearly increasing symptoms for 3 months after after removal of intracanalicular tumors via a retrosigmoid approach, but after one year the situation had significantly improved compared to the initial findings [63].
In 2014, in the context of a cooperative cross-sectional investigation (Mayo, Rochester, and Bergen, Norway), 538 patients with unilateral vestibular schwannoma were asked regarding the symptom of vertigo (Dizziness Handicap Inventory, DHI) [64]. The survey was performed after an average of 7.7 years after first diagnosis. More than half of the patients reported to still suffer from vertigo after that time. Factors associated with a clearly permanent and even severer vertigo were: female gender, higher age of life, tumor size, previous headaches and migraine as well as vestibular symptoms before treatment. Further, persisting vertigo occurred in correlation with the frequency and severity of headaches after treatment. The DHI scores were independent from the aspect if patients had undergone surgery, irradiation, or wait-and-scan.

Tinnitus
The incidence of tinnitus is higher in patients who still have hearing abilities in the affected ear [13]. The occurrence of tinnitus is statistically associated with the tumor growth [42]. Even if the complete removal of a vestibular schwannoma is successful with preservation of the functional hearing ability, the quality of life can be negatively influenced by a tinnitus, newly appearing or deteriorating after surgery [65]. Among 242 patients with vestibular schwannoma included in a survey, 70.7% complained about tinnitus before surgery [66]. After tumor resection via a retrosigmoid approach, the symptom had completely disappeared in 25.5% of the patients, 33.3% had an improved situation, 31.6% observed an unchanged condition, and 9.9% had severer or newly occurring tinnitus. In the same study of 171 patients with preoperative tinnitus, the cochlear nerve was resected in 85 cases (49.7%) and in 86 (50.03%) it was preserved. Between both groups, there was no significant difference with regard to the presence of postoperative tinnitus. A clear pathophysiological explanation of the phenomenon of tinnitus in patients with vestibular schwannoma has not yet been found.

Headaches
The least clarified up to now is the role of headache and its causes. In a mixed series (46% irradiation, 27% surgery, 28% wait-and-scan) of 538 patients,  found headaches of variable incidence and severity in about 50% 8 years after first diagnosis. In comparison to the control group, the patients with vestibular schwannoma complained twice as much about headaches. The treatment modality did not have a significant influence on these percentages, neither had the choice of the surgical approach regarding the long-term risk of severe headaches. Younger patients, patients with higher scores on the anxiety and depression scales, and pre-existing headache diagnoses were the relevant predictors of long-term headaches, the tumor size had not significant influence [67]. It is well-known that headaches of any cause have a major impact on the quality of life. As for vertigo and tinnitus, this factor should be taken into account in the context of information and consultation of patients regarding the therapy options and the long-term treatment. Decision-finding regarding the management of patients with vestibular schwannomas should consider the benign nature of the tumor with mostly slow growth and it should be based on the long-term preservation of the quality of life. Radical tumor resection is certainly justified when a realistic long-term benefit may be expected for the individual patient that outweighs the possible negative effect on the quality of life. On the other hand, the stress of the patient caused by the tumor itself must not be underestimated and the chances of treatment must not be wasted by an unrealistic overemphasis of the risks Apart from single cases, it should be the disease itself and not the decision for the treatment or the treatment modality that determines crucially the patient's quality of life [40], [42]. Already the knowledge of the diagnosis and the natural course of the tumor disease impact the quality of life in the vast majority of the patients [35], [60], [68], [69], [70]. Therapeutic and scientific efforts should aim at preserving the quality of life of the patients suffering from this disease or even at improving it.

Neurofibromatosis type 2
Competent management of patients with the complex disease of NF2, requires a multidisciplinary team including human genetics, neurosurgery, otolaryngology, ophthalmology, neurology, pediatrics, radiology, pathology, radiotherapy, audiology, psycho-oncology, physiotherapy, and other disciplines [71]. The primary objective of medical management must be the preservation of functions because they are inseparably associated with the patients' quality of life. For a reasonable timing of interventions regarding NF2-associated tumors it is essential to know about the growth behavior of the tumors. The tumor growth varies according to the tumor type and location [72], [73] as well as according to individual molecular genetic properties of the tumors [74], [75], [76]. Intracranially, vestibular schwannomas and meningiomas show similar average growth rates between 0.30 and 2.57 cm³ per year [72], [77], [78], [79], mostly, however, clearly less than 10% on average [80], [81]. The most frequently observed growth pattern is a saltatory growth with stable phases, sometimes for years, and growth episodes [7], [72]. The treatment results must be evaluated based on those data. The indication for treatment and definition of the extent of the surgical resection follows more complex criteria compared to spontaneous vestibular schwannomas. Relevant factors hereby are the bilateral hearing function, tumor size, tumor extent in direction of the brainstem and the internal auditory meatus, growth rate, the pa-tient's preferences, and comorbidities. The benefit-risk ratio is clearly defined as the elimination of the functional threat vs. the risk of functional loss by the intervention. Even if surgery of the tumors in NF2 patients is sometimes difficult and complicated, radiotherapy is often no real alternative. Already during 5-years intervals, the tumor control rates (= growth stop and/or shrinking) vary significantly after radiation, probably also independent from the applied radiation dose, between 66 and 100%. Also the hearing preservation rate in those intervals amounts to variable 33-57% [82], [83], [84], [85], [86], [87], [88], [89], [90]. A growth stop induced by radiotherapy in NF2 patients is rarely achieved in comparison to sporadic tumors [91] and especially higher -regarding tumor control more effective -radiation doses can already accelerate the hearing loss in some very few tumors [92]. In cases of NF2, the alternative option of chemotherapy with the VEGF (vascular endothelial grow factor) inhibitor Bevacizumab is useful in some phases. This monoclonal antibody that is applied in Germany as off-label procedure can stabilize the size of vestibular schwannomas over periods of several years and even reduce it [93], [94]. In some cases, the treatment is accompanied by a stabilization or improvement of the hearing ability [95], [96]. The side effects, in particular arterial hypertension and nephrotoxicity, must not be neglected in the long run [97]. Relevant constellations regarding the management in cases of bilateral vestibular schwannomas are displayed in Figure 42. Of course, there are single cases where others than the described management options; the individually adapted strategy requires the involvement of the complete medical and social situation of the patient. As long as a conservative management is reasonably possible, it will generally be preferred in the sense of longterm functional preservation unless there is the microsurgical possibility to remove a small, strategically well located tumor in a bilaterally hearing patient with hearing preservation [20], [98], [99]. In cases of brainstem compressing vestibular schwannomas on both sides and bilaterally functional hearing, in general first a unilateral hearing preserving tumor reduction may be conceived ( Figure 42A). If the hearing ability gets lost during surgery (intraoperative monitoring of evoked brainstem potentials), it is useful to change the strategy and to possibly achieve a complete tumor resection with preservation of the facial nerve function. This would also be the procedure when already before surgery unilateral deafness was found ( Figure 42B). In those cases, it is also useful to discuss with the patient if an auditory brainstem implant should be implanted as socalled "sleeper". If the electric conductivity of the cochlear nerve is preserved, it is generally possible -similar to patients with unilateral spontaneous vestibular schwannoma -to achieve hearing rehabilitation by means of cochlear implantation. While in cases of unilateral or bilateral small vestibular schwannomas, generally wait-and-scan strategy is recommended, it might be useful and also possible in exception-al cases to microsurgically explore such a small tumor and to remove it with hearing preservation ( Figure 42D). Of course further valid treatment scenarios are imaginable, depending on the individual situation of the patient. In cases of large tumors and still functional hearing in one ear and a small tumor with deafness on the contralateral side, it is reasonable to wait as long as the hearing ability remains stable. If the inner ear hearing loss increases in such a case of a growing large tumor, a tumor reduction with hearing preservation, the removal of the posterior wall of the internal auditory meatus, or a therapeutic attempt with Bevacizumab are valid options. If surgery with functional preservation of the facial nerve is not successful in a patient with neurofibromatosis type 2, an immediate transplantation in the same session allows for the best chances for regeneration. A side-toend connection between the hypoglossal and the facial nerves within the first year after paralysis of the facial nerve can still lead to an equally good result regarding rehabilitation of the face [100], [101], [102], [103], [104]. For longer lasting pareses, plastic reconstructions with dynamic temporal muscle transfer, tarsorrhaphy, and eyelid implantations (lid loading) must be discussed. The hearing rehabilitation can be performed in patients with still acoustically useable hearing first with conventional hearing aids. If they are no longer sufficient, the implantation of a cochlear implant (CI; possible in cases of intact hearing nerve and bipolar neurons in the cochlea) or of an ABI (auditory brainstem implant) can be considered according to the individual dynamics of the vestibular schwannoma.